This present invention relates to coherence ultrasound imaging. Ultrasound images are formed by transmitting sound waves from an array and receiving echoes backscattered from the body using the same array. A beamformer applies receive focal delays to the individual channel signals from elements of the array and coherently sums the signals across element channels to form samples representing a scan line. The summed data is then detected and scan converted to form an image, such as B-mode image. For further processing, only the summed signals may be available in many ultrasound systems.
Element channel data may enable alternative beamforming methods that examine the incoming signal across the receiving array. The Van Cittert-Zernike (VCZ) theorem describes the expected coherence of the return signals scattered from diffuse media. For a uniform, diffuse medium, the coherence of echoes backscattered from the focal point as a function of receive element separation, or lag, is given by the Fourier transform of the square of the transmit pressure field magnitude. Therefore, the expected coherence of an aperture with unity weighting across the array is a ramp function that predicts decreasing covariance for increasing lag value. Short-lag spatial coherence (SLSC) imaging takes advantage of the coherence measurement by estimating the coherence curve as a function of lag and integrating the curve up to a small fraction of the aperture length to form an image.
Previous implementations of a real-time SLSC imaging system utilize a research scanner with access to receive channel data. However, translation of coherence methods to more widely-available clinical scanners with more developed post-processing pipelines may not occur. Most clinical scanners do not provide access to receive channel data.